Array Program Help

Hi everyone. This is my first post.

I'm trying to malloc space for a color image in memory, fill it with a design like a colored rectangle, and then write it out into a PPM format file (which will be done in Unix).

As a note, I've had very little experience with 3D arrays. However, I know that the image in memory acts like a 3D array except that the pointers only let you access it one dimension. Any help would be greatly appreciated. I thought this would be a neat thing to try to do (I wanted to ultimately try to make a checkerboard in the long term, but I'm having trouble making a simple colored rectangle, haha).

Below is what I've written so far, I'm kind of stumped on where to go from there. I've commented a section where I believe that the code would go to generate the image.

Code:

---


#include <stdio.h>
#include <stdlib.h>
main(int argc, char *argv[]) {
        unsigned char *image, *tempptr;
        int x, y, c, width, height;
        if(argc < 3) {
                fprintf(stderr, "Usage: %s width height\n", argv[0]);
                exit(1);
        }
        width = atoi(argv[1]);
        height = atoi(argv[2]);
// ***** I believe this is where I should add the code to 
              generate the image and write it 
              out as a PPM file
        return(0);
}

---

Thank you for your help,
James

> However, I know that the image in memory acts like a 3D array
Width and height is 2D - what's the 3rd?

Color would be the 3rd dimension of the array (e.g. a rectangle consisting of values for length and width would be two dimensions and the coloring of it would be the 3rd).


Thanks,
James

No, the color would be the array element value.

Code:

---

pixel[width][height] = someColor;

---

maybe width, height and depth?

Code:

---

// This is a 3d array.
pixel[width][height][depth] = someColor;

---

Depth is just the number of bits used to define a color. 32 bit vs 24 bit vs 16 bit etc.

Hi everyone,

Thank you all for following up with my question. I still am in need of help, but I did not know that depth would be used to define the color, that's very interesting (I stand corrected bithub ;) ).


Thanks again,
James

Hi,

I've made some progress. I can generate the color, but still can't generate the rectangle. Below is my code:

Code:

---

#include <stdio.h>
#include <stdlib.h>


//drawPixel function
//added to simplify drawing loops below
void drawPixel(unsigned char *picPointer, int picWidth, int x, int y, unsigned char
rVal, unsigned char gVal, unsigned char bVal)
{

        picPointer[3*y*picWidth + 3*x] = rVal; //+0 to access red byte
        picPointer[3*y*picWidth + 3*x + 1] = gVal; //+1 to access green byte
        picPointer[3*y*picWidth + 3*x + 2] = bVal; //+2 to access blue byte

return;
}


int main (int argc, char *argv[])
{

if (argc < 3)
{
        fprintf(stderr, "Usage: %s width height\n", argv[0]);
        exit(1);
}

const int wid = atoi(argv[1]);
const int ht = atoi(argv[2]);

unsigned char *picture = (unsigned char *) malloc(3*wid*ht*sizeof(unsigned char));

int x,y;

for(y=0;y<ht;y++)
{

        for(x=0;x<wid;x++)
        {
                drawPixel(picture,wid,x,y,60,100,200); //fills whole image with a light blue
        }

---

As always, any help is greatly appreciated.

Thanks.